In personal computers, computer mice are popular means for inputting data and providing cursor control. A conventional mechanical mouse generally employs a rolling ball and at least two encoder wheels for x- and y-axis input operation. The respective encoder wheels are rotated by the rolling ball when a user moves the mouse along a flat surface, such as a mouse pad. The encoder wheels will intermittently block certain light propagation in the mouse and associated electronic signals are generated to control cursor movement on a computer display. However, the performance of the mechanical mouse may degrade through extended use due to ball abrasion and dust. Moreover, the mechanical mouse uses a bulky and heavy steel ball, which is also inconvenient for the user.
To overcome such drawbacks, optical mice were developed that comprise a light source such as a light emitting diode (LED), a light receiver such as a photo diode and associated components. The conventional optical mouse is operated on a patterned surface for modulating a light emitted from the light source. The modulated light is received by the light receiver to identify mouse movement and control cursor motion.
However, the above-mentioned optical mouse required a specialized mouse pad for normal operation, which limited the applicability thereof. Due to advancement of complementary metal oxide semiconductor (CMOS) image sensors and digital signal processing, a CMOS sensor array can be used in the optical mouse to overcome the above problem. The optical mouse may be operated on a non-transparent flat surface and the detected signals of the CMOS sensor array are analyzed to identify mouse movement and control cursor motion.
For optical mice using a non-coherent light source, such as an LED, the micro-texture of a working surface is discriminated for controlling cursor movement. For optical mice using a coherent light source, such as a laser diode, a complex diffraction pattern, called a speckle pattern, is exploited for controlling cursor movement even when the optical mouse is placed on a mirror like working surface.
U.S. Pat. No. 6,256,016 to Piot et al., entitled “Optical detection system, device, and method utilizing optical matching,” discloses an optical mouse with a coherent light source and uses an artificially limited anisotropic aperture to enhance optical resolution. U.S. Pat. No. 6,246,482 to Kinrot et al., entitled “Optical translation measurement,” discloses an optical mouse with a coherent light source and uses a reference beam produced by a grating to enhance optical resolution. US Patent publication 20040227954 to Xie, entitled “Interferometer based navigation device,” discloses an optical mouse with a coherent light source and uses an interferogram to obtain phase information and to enhance optical resolution. However, in above-mentioned prior art optical mice, complicated optical elements are required and the cost of the optical mouse is increased.
US Patent publication 20040160998 of Gruhlke et al., entitled “Method and apparatus for modifying the spread of a laser beam,” mentions that optical mice containing laser devices are potentially hazardous to the eye. This safety issue is considered by International Standards for The Safety of Laser Products (ISSLP). Class 1 laser devices are defined as being safe under reasonably foreseeable—although perhaps not recommended—conditions of use, such as the use of optical instruments such as a magnifying lens for intra-beam viewing.
US Patent publication 20040160998 also mentions that, according to the ISSLP, the maximum-allowed power, i.e., the acceptable emission light (AEL) level, for a commonly used single-mode 850 nanometer (nm) wavelength Class 1 laser device is 0.78 milliwatts (mW) when measured according to the ISSLP-defined standard. The defined standard is the amount of flux (power per unit area) through a 7 millimeter (mm) aperture in a radial plane that is 14 mm from the point where the laser beam exits the device. Thus, if the flux of the laser beam that passes through the 7 mm aperture is less than 0.78 mW, then the laser device is considered Class 1 safe.
US Patent publication 20040160998 further discloses an optical mouse with a coherent light source and uses an optical train to modify laser beam spread. The laser beam is advantageously spread to prevent a dangerous laser beam with excessive intensity passing through an aperture of the optical mouse to help ensure safety. However, this patent publication employs several complicated optical elements to dilute the light intensity of the laser beam or divert the direction of the optical paths. For example, the patent utilized an optical train element including a focusing lens, a diffractive focusing vortex lens, a beam splitting device or a two dimensional diffraction grating whose cost is expensive.
U.S. Pat. No. 6,704,183 to Stafford et al., entitled “Fault detection in an LED bias circuit,” discloses a bias circuit for preventing excessive emission from light emitting diodes. The disclosure of this patent is hereby incorporated by reference. This disclosure employs two resistors, at least two current legs and several comparators for detecting current passing through an LED; however, the two current legs may consume a lot of power from the LED and thus deteriorate the performance of the LED.
US Patent publication 20050180473 to Brosnan, entitled “Open loop laser power control in optical navigation,” mentions a current output of a drive signal, modulated between two current settings, being applied to a laser diode. This disclosure describes controlling the power consumption of the laser diode by a toggling signal. However, this disclosure requires a complex analog modulator or digital analog converter (DAC) to control the current flowing through the laser diode. Moreover, a plurality of current settings is necessary for this disclosure.
The disclosures of all the abovementioned publications have been incorporated in the parent application by reference.
The abovementioned disclosures provide at least one lens to diminish the emitting power of laser beams which are dangerous to humans' eyes.
According to the present invention, by utilizing a coherent light source, an optical mouse without a lens for diminishing optical power, can be realized. Preferably, a control means is provided to restrict excessive power so that the optical mouse is kept under stable and safe conditions.